The present invention relates to a method of performing fine working which is directed, in metal industries, electronic industries, etc., to performing fine working in a solution through an electrochemical reaction by the use of a probe having a fine tip.
As a method of performing working in a liquid through an electrochemical reaction by the use of a probe having a fine tip, there has heretofore been reported a method of performing working by the use of an electrochemical scan type tunnel microscope.
In a method of performing fine working which is directed to approaching a probe having a fine tip to the surface of a material to be worked and thereby performing fine working by utilizing an electrochemical reaction that occurs between the two, in order to enhance the working precision it is important to decrease the distance between the probe and the material to be worked and maintain this distance to be constant. If the distance between the probe and the material to be worked increases, the working area inconveniently widens. Also, if the distance between the probe and the material to be worked varies during the working operation, it is difficult to shape the worked configuration as predetermined. Since in order for the working precision may be on the order of sub-microns it is necessary for the distance between the forward end of the probe and the material to worked be also be at a level of sub-microns, it is difficult to control such a fine distance with the use of optical means. On account of this, if measurement is performed of the tunnel current that flows between the forward end of the probe and the material to be worked, it becomes possible to control such a fine distance with a high precision relatively easily. While the conventional method of performing fine working that uses an electrochemical scan type tunnel microscope is also arranged to make feedback control of the probe-to-specimen distance by the use of this tunnel current, it involves several problems.
First, there is pointed out the respect that when an electrochemical reaction is caused to occur between the probe and the material to be worked, a Faraday current (electrolytic current) flows between the two. It is difficult to determine whether the current that flows between the probe and the material to be worked is a tunnel current or Faraday current. Also, in the method using feedback control of the probe-to-working-material distance by the use of the tunnel current, there is the problem that when an electrochemical reaction occurs with the result that a Faraday current flows, the distance between the probe and the material to be worked inconveniently varies with the result that the worked configuration diverges from the predetermined configuration. In order to avoid the occurrence of this problem, there can be also considered the use of a method to make the feedback control ineffective at the time of performing the working operation and to fix the Z-axial position of the probe. However, there is a problem in that when working is continuously performed while the probe is being moved, since the distance between the material to be worked and the probe is very short, the probe inconveniently collides with the material to be worked due to the surface roughness thereof, surface inclinations thereof, etc. Also, in a case where the feedback control is performed with the use of a tunnel current, the distance between the material to be worked and the probe must be a magnitude of distance that enables the detection of the relevant tunnel current. Namely, the degree of freedom with which the relevant distance can be set is not high.
Also, since in the process of an electrochemical reaction the amount of reaction is proportionate to the value of the Faraday current, in order to adjust the amount of working it is important to control the Faraday current that flows between the probe and the material to be worked. In the conventional electrochemical scan type tunnel microscope, generally, the probe and the material to be worked operate respectively as working electrodes and an electrochemical cell is constructed with a four-electrode system that comprises these working electrodes and reference and counter electrodes added thereto. In the case of this construction, although the potential of each of the probe and the material to be worked can be independently set, the cell basically is constructed with a main purpose placed on controlling the electrochemical reactions that occur between the probe and counter electrode and between the material to be worked and counter electrode. This means that the cell construction is not made so as to control precisely the Faraday current between the probe and the material to be worked. For this reason, there arises also the problem that it is difficult to adjust the amount of working.